Due to disease, trauma or congenital malformation, the ossicles of the middle ear are sometimes damaged. One common cause is otosclerosis.
The human ear includes three parts, identified generally as the outer ear, the middle ear and the inner ear. The middle ear includes three small bones. The malleus, or hammer, connects to the tympanic membrane, also known as the eardrum, of the outer ear. The malleus is in turn connected to the incus, or anvil. The incus is connected to the stapes, or stirrup. These three small bones are also commonly referred to ossicles or collectively the ossicular chain. The three bones operate as a lever system which amplify force of sound vibrations. The stapes is in turn connected to the oval window of the inner ear. The stapes applies pressure at the oval window which is transmitted to parts of the cochlea of the inner ear. A disease such as otosclerosis can result in fixation of the stapes. This can lessen or eliminate vibration of the stapes resulting in a conductive hearing loss.
One known treatment of otosclerosis and other damage to the stapes is treatment by surgery which replaces the stapes with a prosthesis. The stapes bone is typically reconstructed by creating an opening into the oval window by removal of a portion or all of the damaged stapes. The stapes prosthesis is placed into the newly created opening. The prosthesis is attached to a remaining middle ear ossicle, referred to as the anchoring ossicle, so that sound vibrations are transmitted from the ear drum to the oval window opening.
A typical stapes prosthesis consists primarily of two components. The first is a cylindrical portion, often referred to as a piston, designed to fit into the oval window opening. An attachment mechanism which may be a wire bent into the shape of a shepherd's hook, a plastic doughnut shaped member, or a cup, is attached to the cylindrical portion and is designed to be crimped or closed around the anchoring ossicle. Such attachment mechanisms are typically difficult to close properly around the anchoring ossicle. The opportunity for physicians to practice the closure technique is limited. If the attachment mechanism is closed improperly, the prosthesis will be either too loose, resulting in a poor hearing result, or too tight, resulting in destruction of the ossicle to which it is attached. Some stapes prosthesis consist of a plastic loop which require the surgeon to open the loop prior to insertion which causes permanent plastic deformation. After implantation, the surgeon must still close the device to ensure firm attachment. The axis of the long process of the incus is seldom perpendicular to the central axis of the oval window opening. As a result, any improper alignment can render the prosthesis prone to loosening. Additionally, known prosthesis devices may be difficult to remove if revision is desired.
The present invention is directed to improvements in attachment mechanisms for middle ear prosthesis.